The aim of this research is to trace the early development of attentional systems and to relate these developments to the control of action and emotion. Using marker tasks identified in adult patients and by neural imaging, the applicants are able to relate behavioral findings to underlying neural systems. In the proposed project they trace the development of an executive attention network that has been linked to frontal lobe development. There is reason to believe that this network plays a fundamental role, not only in the development of high level cognitive capacities, but in the self-regulation of emotional states and action. Because attentional self-regulation can result in behavior problems and difficulties in school, research tracing the normal development of, and individual differences in, these controls has important implications for society. Two marker tasks are employed in this project involving 24 to 36 month olds. The first is a spatial Stroop-like task investigating the resolution of conflicts between location and stimulus identity. The second involves learning sequences of locations where the correctness of the association depends on context. Both of these tasks trace the ability to deal with competing response tendencies, a basic component of the executive attention network. Their preliminary data show that these tasks can be made appropriate to measure the performance of children of this age and that they undergo important changes in this period. The first study, a cross-sectional study of 24, 30, and 36 month olds will attempt to replicate the stage-like development of performance on the Stroop task that was found earlier and to relate development of sequence learning to the Stroop performance. In addition, cluster analyses will be performed on the 30 month olds (with additional 30 month old subjects added) to examine the development of attentional mechanisms at this transition age. Following this cross-sectional study, a longitudinal study will be performed examining 30 month old children on the Stroop, Sequence learning and a battery of inhibitory control tasks. The children will be tested every 2 months between 30 and 36 months. In both studies, parent report measures of attention and inhibitory control will also be obtained, along with measures of negative emotionality.